1. Field of the Invention
The present invention relates to an image forming apparatus, such as a facsimile, a laser printer or a copying machine, to which electrophotography is applied, and more particularly to an image forming apparatus and an image forming method, which can execute a control to enable toner replenishment (toner bottle replacement) while continuing a printing operation without a halt when printing is being effected.
2. Description of the Related Art
In general, an image forming apparatus, such as a facsimile, a laser printer or a copying machine, to which electrophotography is applied, includes an image forming section that applies toner to an electrostatic latent image, which is formed on the surface of a photoconductor drum, and forms a visible toner image. The toner image, which is formed on the surface of the photoconductor drum by a developing unit that is a part of the image forming section, is transferred to paper by a transfer unit. The paper with the transferred toner image is conveyed to a fixing unit, and the toner image is fixed on the paper by a fixing device of the fixing unit.
In the prior-art image forming apparatus, the developing unit is provided with a sensor for detecting the amount of toner. If the sensor detects that the toner amount is a preset value or less, the image forming apparatus executes a control not to perform a further printing operation in order to prevent a decrease in density of a print image, to display a message prompting the user to replenish toner, and to stop a printing operation until the toner replenishment is completed.
In recent years, many users execute large-volume printing with an increase in operation speed of the image forming apparatuses. Hence, there is a demand for increasing productivity by decreasing an idle time of the image forming apparatus due to a shortage of toner.
In order to meet this demand, a modern image forming apparatus comprises a developing unit that forms an image on a photoconductor drum using toner; a storage unit that stores toner that is to be supplied to the developing unit; a first supply unit that supplies toner from the storage unit to the developing unit; a first drive unit for driving the first supply unit; a toner bottle that contains toner and is detachably attached to the image forming apparatus; a second supply unit that supplies the toner in the toner bottle to storage unit; a second drive unit for driving the second supply unit; a first door that is openably/closably provided to remove the toner bottle; and a first sensor unit that senses the opening/closing of the first door. While the first sensor unit detects that the first door is open, the first drive unit and developing unit are controlled to be operable and the second drive unit is controlled to be inoperable.
When the toner bottle is to be taken out, the second drive unit is controlled to be inoperable on the basis of the detection result that the first door is opened. Thus, the operation of the second supply unit is stopped, and the toner bottle is not rotated and can easily be taken out. In addition, at this time, the first drive unit and developing unit are controlled to be operable. Therefore, the printing operation can be continued.
However, in this type of image forming apparatus, when the first door is opened, the printing operation is continued in the state in which the supply of toner from the toner bottle to the storage unit is stopped. Consequently, the toner in the storage unit may decrease to a predetermined amount, and the image density may lower.
Furthermore, when the first door remains opened, the temperature in the image forming apparatus lowers and the turn-on time of the heater of the fixing unit increases, leading to an increase in power consumption.
To solve these problems, a technique has been disclosed, wherein the operation of the image forming section is stopped if closing of the first door is not detected by the first sensing unit within a predetermined time period after the detection of the opening of the first door by the first sensing unit.
Jpn. Pat. Appln. KOKAI Publication No. 2003-114567, for instance, discloses a technique wherein the printing operation is stopped if a time period in which the first door is opened exceeds a predetermined value. However, in some cases, the printing operation is performed in the state in which the first door is opened, and the printing operation is stopped despite that the amount of toner in the storage unit has not yet been consumed to a predetermined level and no decrease has occurred in the density of print images. In addition, there is such a problem that if a great number of images with a high print ratio are printed after the first door is opened, the amount of toner in the storage unit decreases below a predetermined level before a predetermined time period expires, resulting in a decrease in image density.
Besides, the modern image forming apparatus includes a tray paper feed unit having a plurality of stages (e.g. trays 1–3) and a manual paper feed unit. In most of image forming apparatuses of this type, different print speeds per minute are set for the respective paper feed units. For example, tray 1 permits printing of 60 A4-size sheets per minute, tray 3 permits printing of 50 A4-size sheets per minute, and the manual paper feed unit permits printing of only 30 A4-size sheets per minute.
In this type of image forming apparatus, when continuous paper-feed printing is performed with the paper feed unit (e.g. tray 1) having a high printing speed per minute, there may be a case where the amount of toner in the storage unit decreases to a predetermined level while the time period in which the first door is opened is within a predetermined time range. This leads to a decrease in image density. On the other hand, when continuous paper-feed printing is performed with the paper feed unit (manual paper feed unit) having a low printing speed per minute, there may arise such a problem that more than a predetermined amount of toner still remains in the storage unit even when the time period in which the first door is opened is within a predetermined time range, and the operation of the image forming apparatus is stopped despite that printing with normal image density can be performed.